A technique of transmitting power by using electromagnetic waves (microwaves) and supplying the power in a wireless manner has been developing in recent years. As an example of a wireless power supply technique by electromagnetic waves, there is a system in which magnetic coupling and resonance are used in a short distance of several meters or less, such as in electromagnetic induction and magnetic resonance, by using microwaves in a frequency band from several 100 kHz to several MHz. In such a system, a wireless power transmission method in which a power receiving device to which the power is supplied is fixed at a constant position from the power supply device which transmits the power. A method of moving the position of a power transmission antenna in accordance with the power transmission position for transmitting the power by wireless with respect to a target in which the position of the power transmission position varies due to movement of the power receiving device existing in a short distance.
On the other hand, as a method of transmitting the power by wireless to a target in which the power transmission position varies in a case where a distance from the power transmission device to the power receiving device is long and the power receiving device is in a far distance, there exists a system of transmitting the power by using microwaves. It is possible to transmit microwaves to the power receiving device over a far distance by using microwaves in a range from several hundred MHz to several GHz. As examples of such wireless power transmission systems, there are proposed, for example, a cosmic solar power generation system in which an artificial satellite having solar power panels is launched above the equator and the power generated by solar light is transmitted to the power receiving device on earth, a system of transmitting the power to the power receiving device arranged in a far isolated island and other systems.
The wireless power transmission device by using microwaves can transmit the power to a target in which the position of the power receiving device varies in principle. As the power transmission method in the above case, there is a method in which, when the power transmission position varies or when there are plural power transmission positions, the transmission side recognizes the position of the power receiving device and transmits the power so that phases of the power to be transmitted are aligned at the position. It is possible to transmit the power efficiently by using the wireless power transmission method. As a specific example, there is a wireless power transmission device in which pilot signals from a power receiving antenna of a power receiving device are received by a power transmission antenna of a power supply device for recognizing the position of the power receiving device and the power supply device controls phases of the power based on the received information (for example, refer to JP-A-2006-287451 (Patent Document 1).